38 DGAS, charcoal canister & stock jet sizes

[cygnus x-1]

Hey Guys,

Thanks for the link. They also have a PP2 sensor as well, for $35 more, doesn't sound so bad if it's got internal logging.

Is it worth being able to log while driving, though?

Logging while driving is the most useful part of logging. The PP2 may be a little more convenient since you don't need a laptop running while driving; just need it to pull the data later.

The PP2 is $85 if you want to one with the sensor included.

There's no stumble, unless I put my idle under 1k rpm, and if I use the brakes, and the engine fan comes on, it will bog.

That's pretty normal.

I used the idle adjust screw to crack the throttle plates open about 3/16 turns in, and it holds idle at 1k, and doesn't bog. The mixture screws are both set 7/8 turns out, so I think those were set well.

Sounds about right.

If I understand it correctly, the way the weber works, is that at idle, with the transition fuel holes mostly covered by the throttle plates, the engine runs off the mixture supplied by the mixture screws, and whatever air coming into the carb through the throttle plates (right?)

Assuming that is right, the low speed circuit runs when the throttle plate is opened by pushing the gas pedal, which pours fuel in through the transition holes that are normally covered by the plates. This, of course, is in addition to the fuel already coming through the mixture screws at the bottom of the barrels.

Both of these fuel outlets are fed by the idle fuel jets (in my case, labeled "main choke idle jet" and "left side jet" based off the jetting box).

Around 3-3.5k rpm, the idle fuel jets are unable to supply enough fuel to get the engine to run more, so the main jet's start to kick in. During the transition phase, the engine is actually pulling fuel from all 3 sources, and as the rpm climbs out of the transition phase, the low speed circuit stops putting fuel through the idle jets, and the main circuit compromising of the main fuel and main air corrector jets, does all the work (This is the part I'm not sure of, since I assumed they all keep working all the way to the top, how can you just "switch off" a fuel supply? vacuum signal???)

You've got it. I think the the idle circuit is always supplying fuel, but at full throttle it's so insignificant that it just doesn't matter.

Also, the guide linked above mentions that the idle circuit has a set of idle air correctors as well? I haven't seen these on my weber, so maybe that's just a holley/edelbrock thing...

The 38 doesn't have idle air correctors, but other Webers might. Don't know really.

So , starting with the idle off of choke: I think it's too rich. Not too much fuel, but the choke plates are closed all the way when the cam is released. I'm thinking I should set them to be open a little bit to allow more air in on start, since the belching black smoke problem goes away when it start to open (I assume black smoke = too rich).

Yeah, you need to adjust the choke. Lots of stuff out there on how to do that so I won't go into it here. (and it's been so long I can't remember exactly how to do it. )

Next, the idle is fine. I am not sure what indicates a "lean burn" out of the tail pipe, but I've heard that lean burn = lots of hydro carbons, and my exhaust at idle is very "wet" after it goes through my catalytic convert.. maybe lean??

Too lean means not enough fuel, which would produce minimal unburned hydrocarbons in the exhaust. The wetness you see is water that has condensed in the tail pipe, and is totally normal. Water and CO2 are the main products of combustion, along with a little CO (carbon monoxide), unburned hydrocarbons (fuel), and nitrogen oxides (NOx).

I wouldn't worry too much about the idle mixture. In my experience these engines really like the idle to be rich, so you might smell a little fuel at the tailpipe while it's idling. Just tune it so the idle is the most stable, and produces the strongest vacuum signal at a given RPM. Unless you leave your car idling a lot it has minimal effect on fuel mileage.

The low speed circuit runs fine... I think. It pulls ok if I push the throttle in maybe 20-25%. If I start to push it harder, it doesn't really make much of a difference, throughout the low speed circuit, which ends a little bit over 3k rpm (I'm assuming my high-speed circuit comes on 3.5k - 4k rpm).

I'm thinking my main circuit is way lean though. if I "punch" it off of a start, I have less power than my low speed circuit makes. I'm thinking that when I open the throttle plates all the way, there's so much air that the mixture is too rich. With a WOT start, (i.e, I get it rolling in 1st, and then floor it) it has less power than if I'd just crack the throttle open 20-25%.. Kind of lame considering that I heard the weber was "burning rubber in 1st gear" if you'd punch it, lol!

My main question here is... how do I know if it's lean, aside from the wideband sensor and an emissions test?

You know it either by experience, or by using the old school method of reading the spark plugs. Reading plugs for tuning is mostly a lost art because wideband O2 sensors are cheap and so much easier, but there is still plenty of info out there on how to do it.

It does sound like maybe you need bigger main jets or maybe a smaller air corrector. If you have a jetting kit you could change out the jets and see what happens.

Timing:

I read some posts from others saying that with the weber, the timing needs to be advanced, maybe 5-10 degrees, if not more?

However, I'm not sure if I'm advancing it properly, since my engine seems to be running weird the first time I "advanced" it.

With my timing light, I found the regular timing mark with my idle set on the Weber, and it doesn't run too bad. Feels a lot closer to how the stock carb is running.

However, seeing as how I have vacuum applied to both ports on the distributor (the lower one, further out from the engine is actually a "cold start" vacuum advance that advances timing when the water is below 51 degrees C) I'm thinking that under higher manifold vacuum, the timing is getting advanced further than before...

Having both distributor ports connected will advance the timing an extra 4 degrees all the time.

When I advanced my timing, I slid the distributor a bit "up" (counter-clockwise, when looking at the cap) and the timing marks went "up" in comparison to the fixed marker on the block. I set it so that the bottom hash mark on the flywheel was about 1/2" higher than where the pointer was at. It wasn't pinging or backfiring at that setting, but when I drove it around, it didn't really feel "right"... The rpm at idle did go up a bit though, which also gave me a bit of a problem when I'd start out at a light, since it seemed like it was bogging down when I was trying to get it rolling in the gear. I assumed at the time that it was just me sucking with driving a stick after 2 weeks of no practice, but now that I reset the timing so that the pointer is on the lower of the 3 hash marks, it is working much more closely to how I expect it to be.

My question here is: A. Am I advancing the timing correctly? I was guessing as to how much travel "5-10 degrees" would actually be on the flywheel, and going off of the pointers, but this isn't really an exact approach here... & B: which way is "Advance", and what kind of effect should I be seeing if I've correctly advanced the timing?

My motor is bone stock, so I'm just looking for how to get the motor running the best, but if the weber does require a different timing point then what the timing markers on the flywheel delineate, then I want to get it right so I don't damage my motor

It doesn't require the timing to be advanced, but many people find that a little more advance gives better throttle response. If when you advance the distributor, it gets twitchy (hard to describe but to me it feels like the engine is nervous) or just doesn't "feel right", then it's probably too much. You are advancing the distributor correctly, it just sounds like you went a little too far. No big deal, just find the spot where it seems the best and leave it. Without a dyno to measure engine output it's about the best you can do.

The common method of 'advancing the timing until it pings, and then back off a bit' doesn't seem to work with these engines. They are very knock resistant (I think because of the head design) so the only indication you get of too much timing is how the engine feels.


C|

[88Sleeper]

Hi Cygnus, thanks for the useful info! Makes me feel better I'm not down the wrong path completely

Just a quick update, I managed to get it running identical to the way my stock carb was, but I'm a tad worried about the timing advance still.

So, here's what I did:
hesitation issue -> I changed the vacuum advance to run off of the distributor port on the carb, not manifold vacuum (I'm going to get flack for this, I know it... more on this below)

Lean Burn -> I changed my main jets from 145 to 150. Based on the spark plug tuning, I think it's perfect. The "6" heat range NGK plugs I got show a thin brownish ring right at the tip of the ceramic where it meets the central electrode now, instead of being completely bone-white, and the "jetting" ring is completely black (it was only 3/4 black before, which means lean I guess). The car also responded much better once the main circuit is engaged (no more, "I feel like a dying horse" feeling).

So for the advance.

My timing on my stock carb was set 2/3 of the way to the max limit of distributor advance with the stock carb. The stock setup pulls advance from manifold vacuum. BUT I had major vacuum leaks everywhere (based on my testing of the idle circuit components, etc.) With manifold vacuum on the weber, my distributor was actually RETARDED!! (the "middle marker" dot on the distributor bolt flange that tells you the middle ground between retarded and advanced was on the retarded side by a bit. This was at 1krpm idle with manifold vacuum, and the timing marks centered in the flywheel)

Due to the timing being retarded, when I would go WOT, my car wouldn't rev over 5.5k rpm without sucking fuel like a MOFO (I found I only got 24mpg at the pump when I checked after 200 mi).
It was also causing me huge hesitation issues when I'd open the throttle to put it into gear.. It didn't die necessarily, but I almost got nailed by a semi when I changed lanes and "punched it" only to sputter for about 3 seconds, thinking I was going to get my ass scrunched up nice.... I know it wasn't due to bogging down from too much fuel in the accelerator pump, since I have to slam it really fast to do that...

Solution -> I changed my vac advance to the port on the carb, and plugged the manifold vac source. once I did that, I reset the timing, and found that it landed on my timing marks perfectly at the same point as the stock carb did (I've got a wear mark on the flange, so I know I'm within .5 mm on the same spot)

The hesitation is almost completely gone now. Not all the way, since if I try hard enough, I can feel it, but for 80% of my driving, it is un-noticeable.

My concern -> When I "go" I am not sure if I have a knock or not. This is because there is now full-vacuum being applied to the vac advance when I accelerate, instead of the weak vac signal it was getting before. It pulls EXACTLY like it did before, with maybe a hint more of a fast "chugga-chuga" train sound when pulling on the upper gears. My gut feeling says the timing is a tad bit too early due to the much higher vac signal, but there's no knocking or pinging sound on this sucker!!? T.T

Spark Plug question -> I had Bosch Wx9 something plugs in there, and I put NGK FR6-something plugs in there now. My main question is whether or not cold plugs are better for the older motor? Sometimes when i shut the motor off, it diesels maybe once when I shut it down... I know that without the idle solenoid to plug the transition port on the stock carb, mine would diesel until I would cut it with the clutch & gear (great way of knowing when the solenoid is bad... not, lol) This weber doesn't have one, and I'd rather not switch to one if I have to replace the main idle jet... but I'm wondering if a hot plug is causing me the diesel? With the advanced timing, if it does diesel, it fires off once and only once, and then I get a noise like air getting shot back out through the carb (makes me think the piston gets thrown the other way when this happens).

Actual occurrence rate is maybe 1 in 5 shut-downs this happens, and it doesn't matter if I shut down at idle, or low-high rpm.
It started after I opened the throttle plates a bit more to get higher idle at start since my lights would cause idle bogging when I ran them, but it happens a tad less when I turned it down a hair.
Is it normal for the idle to hold steady, maybe +50 rpm when the engine is fully warmed up vs cold/still warming the water?

[other stuff]:
I've got this rattle in the engine bay that came up now. Before I did the carb, the only noise I had was a sticky lifter type noise that would go away after it warmed up a bit.

I can't hear that anymore, but I've been dealing with a plasticy rattle noise now. Last night I found one of the timing cover bolts was coming loose, and that helped some, but I almost feel like the spring on the timing belt tensioner is loose (I did that a month before the carb). I haven't confirmed yet, but I don't know if I should be worried if the spring comes loose, considering that the bearing is held in place by a bolt? I checked the belt for tension when I found teh loose plastic cover bolt, and it's still nice and snug (maybe 1-2mm of play) on the tensioner side, & the front side of the belt (left side of camshaft gear) is solidly tight (no budge).

The noise is driving me nuts. and I can't find it. It comes from the driver side of the motor, but I guess this issue is up for a different thread...

Thank you and lostforawhile in getting this swap done! I really love the weber, but to be honest, I'm seeing performance being equal, maybe a hair better in the low-end with the 38, but I traded 32/40 mpg average for what I'm thinking will come out to 28/?? average now..

Sorry for the long post, but having a hard time finding the time to write...

[cygnus x-1]

Just a quick update, I managed to get it running identical to the way my stock carb was, but I'm a tad worried about the timing advance still.
So, here's what I did:
hesitation issue -> I changed the vacuum advance to run off of the distributor port on the carb, not manifold vacuum (I'm going to get flack for this, I know it... more on this below)

Something is still not right, because it needs full vacuum advance at idle. With the throttle ported vacuum you won't get that.

Lean Burn -> I changed my main jets from 145 to 150. Based on the spark plug tuning, I think it's perfect. The "6" heat range NGK plugs I got show a thin brownish ring right at the tip of the ceramic where it meets the central electrode now, instead of being completely bone-white, and the "jetting" ring is completely black (it was only 3/4 black before, which means lean I guess). The car also responded much better once the main circuit is engaged (no more, "I feel like a dying horse" feeling).

That sounds better. I would try going to 155 just to see what happens.

My timing on my stock carb was set 2/3 of the way to the max limit of distributor advance with the stock carb. The stock setup pulls advance from manifold vacuum. BUT I had major vacuum leaks everywhere (based on my testing of the idle circuit components, etc.) With manifold vacuum on the weber, my distributor was actually RETARDED!! (the "middle marker" dot on the distributor bolt flange that tells you the middle ground between retarded and advanced was on the retarded side by a bit. This was at 1krpm idle with manifold vacuum, and the timing marks centered in the flywheel)

Due to the timing being retarded, when I would go WOT, my car wouldn't rev over 5.5k rpm without sucking fuel like a MOFO (I found I only got 24mpg at the pump when I checked after 200 mi).
It was also causing me huge hesitation issues when I'd open the throttle to put it into gear.. It didn't die necessarily, but I almost got nailed by a semi when I changed lanes and "punched it" only to sputter for about 3 seconds, thinking I was going to get my ass scrunched up nice.... I know it wasn't due to bogging down from too much fuel in the accelerator pump, since I have to slam it really fast to do that...

Solution -> I changed my vac advance to the port on the carb, and plugged the manifold vac source. once I did that, I reset the timing, and found that it landed on my timing marks perfectly at the same point as the stock carb did (I've got a wear mark on the flange, so I know I'm within .5 mm on the same spot)

The hesitation is almost completely gone now. Not all the way, since if I try hard enough, I can feel it, but for 80% of my driving, it is un-noticeable.

My concern -> When I "go" I am not sure if I have a knock or not. This is because there is now full-vacuum being applied to the vac advance when I accelerate, instead of the weak vac signal it was getting before. It pulls EXACTLY like it did before, with maybe a hint more of a fast "chugga-chuga" train sound when pulling on the upper gears. My gut feeling says the timing is a tad bit too early due to the much higher vac signal, but there's no knocking or pinging sound on this sucker!!? T.T

Spark Plug question -> I had Bosch Wx9 something plugs in there, and I put NGK FR6-something plugs in there now. My main question is whether or not cold plugs are better for the older motor? Sometimes when i shut the motor off, it diesels maybe once when I shut it down... I know that without the idle solenoid to plug the transition port on the stock carb, mine would diesel until I would cut it with the clutch & gear (great way of knowing when the solenoid is bad... not, lol) This weber doesn't have one, and I'd rather not switch to one if I have to replace the main idle jet... but I'm wondering if a hot plug is causing me the diesel? With the advanced timing, if it does diesel, it fires off once and only once, and then I get a noise like air getting shot back out through the carb (makes me think the piston gets thrown the other way when this happens).

Actual occurrence rate is maybe 1 in 5 shut-downs this happens, and it doesn't matter if I shut down at idle, or low-high rpm.
It started after I opened the throttle plates a bit more to get higher idle at start since my lights would cause idle bogging when I ran them, but it happens a tad less when I turned it down a hair.
Is it normal for the idle to hold steady, maybe +50 rpm when the engine is fully warmed up vs cold/still warming the water?

[other stuff]:
I can't hear that anymore, but I've been dealing with a plasticy rattle noise now. Last night I found one of the timing cover bolts was coming loose, and that helped some, but I almost feel like the spring on the timing belt tensioner is loose (I did that a month before the carb). I haven't confirmed yet, but I don't know if I should be worried if the spring comes loose, considering that the bearing is held in place by a bolt? I checked the belt for tension when I found teh loose plastic cover bolt, and it's still nice and snug (maybe 1-2mm of play) on the tensioner side, & the front side of the belt (left side of camshaft gear) is solidly tight (no budge).

Thank you and lostforawhile in getting this swap done! I really love the weber, but to be honest, I'm seeing performance being equal, maybe a hair better in the low-end with the 38, but I traded 32/40 mpg average for what I'm thinking will come out to 28/?? average now..

Based on all of the above I'm going to say that the cam timing might be off by one tooth. Try turning the crank counter-clockwise (looking at the crank pulley) until the mark on the flywheel indicates TDC exactly. Then look at the cam pulley and see of the two marks are lined up with the valve cover mounting surface. It's fairly common for the belt to be off one tooth.

With the cam timing verified correct, check the distributor timing. The position of the distributor itself is not really important and varies a bit from engine to engine. What matters is that the plugs are firing at the correct time. There should be two marks on the flywheel, one for TDC and one for the correct idle timing (with vac advance connected). If the idle speed is set higher than what the specs say, turn it down to spec to set the timing, then turn it back up. With the idle at 1000RPM you might get a little mechanical advance which would change the setting.

Also check the advance diaphragm on the distributor to make sure it isn't leaking. It should hold vacuum perfectly, although you could probably live with a very small amount of leaking.


C|

[88Sleeper]

Ok, I will try that.

I know the cam timing is good. I just did the valve clearance last night since I remembered that the Boise is coming from around the no. 1 piston in the valve train. Everything checked out though, the valves had more clearance than spec, but I set it up.

I'm going to take the belts off one by one to see if its a bearing on one of the accessories, but I have a gut feeling that the "stuck lifter" noise I had was actually a rod bearing, and now it's smashing against my valves and head at TDC.

That doesn't explain the burning rubber smell though when I stop. It fills the cab when the fan is on. I know it's not burning oil. I fixed all of my oil leaks and it's not eating oil at all at the moment. My brother also confirmed it smells like rubber, so I'm thinking it's a belt or bearing. The belts are tight... maybe too tight? (They have 0 slack but one of the suckers still squeals at start -_-'

Thx

[88Sleeper]

Found it...

I actually can't believe I was able to drive on this for over 2 weeks. It had slack on the car, but fell apart soon as I loosened the bolts.

It's the water pump pulley wheel

[88Sleeper]

Well, with the new pulley, there's no noise, but it still smells like burning something when I shut it down... any ideas?

Also went to the pump... 25 mpg mixed driving, so a 7mpg loss with the 38/38. But yes, there is much more tq now; the engine doesn't like to give up rpm so easily like with the keihin.

Would running ported vacuum cause me worse mileage? I'm sorry but I just can't seem to understand why manifold vac is preferred since it causes more hesitation when vacuum is lost when throttle plates are cracked open initially (makes it hard to start moving/clutch into gear 1 w/o almost stalling).

With the ported setup, it is much easier, but yes, there is still some hesitation, but much much less than manifold vac.

[88Sleeper]

Oh, also in response to cygnus post, at idle, with vac advance connected, my timing is set to the middle of the 3 marks on the flywheel, just like it was w/stock.

Car pulls good, and I don't feel like it is knocking at all, but I still can't rev over 6.5k rpm (& even then, it crawls up there from 5.5k rpm, slow gains), even in gear 1.

Most of the power feels to be in the 3.5 -5.5k rpm range. I'm wondering if I need 1 size larger main air corrector, since that is what controls the A/F mix at the upper rpm limit?

Only thing is it has 170's now, and the kits lowest is 190's

[lostforawhile]

Oh, also in response to cygnus post, at idle, with vac advance connected, my timing is set to the middle of the 3 marks on the flywheel, just like it was w/stock.

Car pulls good, and I don't feel like it is knocking at all, but I still can't rev over 6.5k rpm (& even then, it crawls up there from 5.5k rpm, slow gains), even in gear 1.

Most of the power feels to be in the 3.5 -5.5k rpm range. I'm wondering if I need 1 size larger main air corrector, since that is what controls the A/F mix at the upper rpm limit?

Only thing is it has 170's now, and the kits lowest is 190's

are you running a stock cam? if you want to move the power band up much you will need a different cam, or are you saying it's not revving very fast?

[Dr_Snooz]

If you're running your vacuum advance off a ported vacuum source and then setting your timing by that, your timing is going to be wildly off at any RPM above idle. Ported vacuum was designed and used on some American cars as a way to pass smog tests without having to design a more efficient engine. It did so by drastically changing timing at idle without affecting it at other engine speeds. Japanese cars never used it. You definitely want to use manifold vac and then tune everything else accordingly. Using ported vac is only going to mask other maladjustments in your setup.

[88Sleeper]

If you're running your vacuum advance off a ported vacuum source and then setting your timing by that, your timing is going to be wildly off at any RPM above idle. Ported vacuum was designed and used on some American cars as a way to pass smog tests without having to design a more efficient engine. It did so by drastically changing timing at idle without affecting it at other engine speeds. Japanese cars never used it. You definitely want to use manifold vac and then tune everything else accordingly. Using ported vac is only going to mask other maladjustments in your setup.

Looks like it's back to the drawing board for me.

I originally tried it since I found a page from a guy posting as a weber tuning tech that they intended the disy. advance during swaps to be run off the ported vacuum pipe on the back of the carb.

[88Sleeper]

are you running a stock cam? if you want to move the power band up much you will need a different cam, or are you saying it's not revving very fast?

I have a stock cam, but really looking to upgrade, but to get the motor to rev like it used to.

Normally if I gave it WOT I'm 1st gear, it would shoot right up to 8k rpm.

The weber shoots up to 5.5k and then crawls up to 6.5k-7k from there, but it tops out at 7k...

[88Sleeper]

Overall, do you guys with the webers have bad
hesitation with manifold vac advance?

I heard bad A/F mix will make for poor response, but theoretically, I don't see it having as much impact for fixing hesitation...?

[2oodoor]

I never had hesitation with the 38, but I will say that they do get flat with an automatic trans after 6800. Make sure you have full throttle with your linkage, it may not even be pegged when you think it is.
I use 60 idle jet and sometimes 65 when the weather gets cooler. I like the 38 because it's instant rev and gets there quick, also it pulls strong from a low rpm if you using a manual tranny.
Something else that I think holds back a 38, that cheezy air filter set up they come with. I got a significant improvement using the 5 inch adapter that permits you to use a standard low profile 4bbl air cleaner.
A #70 squirter accelerator pump jet works wonders too.
I never used vacuum advance at all with my 38 set ups, I run a bit more base distributor advance but remmber you have to consider that is another factor in the best idle adjustment procedures, get as low rpm as it will take with idle stop screw.

[lostforawhile]

Looks like it's back to the drawing board for me.

I originally tried it since I found a page from a guy posting as a weber tuning tech that they intended the disy. advance during swaps to be run off the ported vacuum pipe on the back of the carb.

remember the advance on these dizzys is calibrated for manifold vacuum, I know on the carb setup I have from the Datsun, it has a ported vacuum nipple, but I'm just going to set up the dizzy as it was originally designed

[Oldblueaccord]

I have a stock cam, but really looking to upgrade, but to get the motor to rev like it used to.

Normally if I gave it WOT I'm 1st gear, it would shoot right up to 8k rpm.

The weber shoots up to 5.5k and then crawls up to 6.5k-7k from there, but it tops out at 7k...

I never tune a carb with vacuum advance hooked up on any vehicle. Very likely you have to much advance at high rpms and your lean also. This is a trip to blowing a motor.

Never ever force a motor to rpm up past were it wants. Either it being held back mechanically or thru induction. The only outcome is bad. Nothing good is going to happen by forcing the issue.

Edit: pull a spark plug and see where your at tuning wise. Its easy and cheap. There pictures online you can use to compare.